US warplanes continue to fire off air strikes in northern Iraq destroying militant artillery and killing some insurgents.

The bombings have allowed US forces to start humanitarian efforts, with combat jets dropping bundles of food and fresh drinking water to thousands of Iraqi citizens, trapped on a mountain top by the militants.

The United Nations was also urgently preparing a humanitarian corridor as the Federal Government offers Iraqi refugees priority placements in Australia’s humanitarian refugee intake.

An armoured vehicle belonging to Kurdish Peshmerga fighters rushes to a bombing site as smoke rises after airstrikes targeting Islamic State militants near the Khazer checkpoint outside of the city of Irbil in northern Iraq. Picture: APSource:AP

Australia has also upped its travel alert for Iraq to its most serious level — do not travel.

Laser-guided bombs, each weighing 227kg, have destroyed convoys belonging to jihadist group Islamic State militants.

Drones, remote piloted aircraft, are also being used and have struck a terrorists mortar position.

When Islamic State fighters returned to the site moments later they were attacked again and killed.

US President Barack Obama authorised the air strikes after Islamic State militants, which list about 60 Australians among its fighters, maintained a relentless two-month jihadist offensive, rampaging across northern Iraq and kicking tens of thousands from religious minorities out of their towns and villages.

Extremists have also taken hundreds of women captive and are treating them as slaves while families have been rounded up and slaughtered in mass executions.

The UN believes more than 500,000 people have been displaced by the violence since June, bringing the total this year top more than one million.

President Barack Obama speaks about the situation in Iraq in the White House. Picture: APSource:AP

Several thousand others have had their lives threatened.

Australian Foreign Minister Julie Bishop backed the actions of the US in launching air strikes and said they were necessary to end the attacks by terrorists.

She said there was a humanitarian disaster unfolding in Iraq and the Government would assist the Iraqi government with whatever resources or assistance it needed, including political dialogue.

“We believe the humanitarian disaster in Iraq must cease so we support international efforts including the actions of the United States, to bring this to an end,’’ she said.

“We are also deeply concerned that the conflict in northern Iraq is attracting Australian citizens to the region to train with this terrorist organisation to carry out terrorist activities in Iraq, but

equally worrying to return to Australia with the skills and capability of carrying out terrorist activities in Australia.”

Mr Obama said despite his vows to end the war in Iraq he needed to step in to avert what he dubbed a looming “genocide”.

They are his first ordered air strikes on Iraq since he withdrew troops in 2011 after a long and bloody occupation.

White House and the Pentagon officials said the strikes would be limited and the bombings would focus on situations where US forces or personnel could be in jeopardy and designed to deter the Islamic State.

Kurdish Peshmerga fighters stand guard during airstrikes by the US forces targeting Islamic State militants at the Khazer checkpoint outside of the city of Irbil in northern Iraq. Picture: APSource:AP

“As the president made clear, the United States military will continue to take direct action against (the Islamic State) when they threaten our personnel and facilities,” the Pentagon said.

US Secretary of State John Kerry said the extremists’ had embarked on a “campaign of terror against the innocent” and the “grotesque and targeted acts of violence” had the hallmarks of genocide.

“For anyone who needed a wake-up call, this is it,” Mr Kerry said.

The US military action is permitted in a least three locations: Baghdad, home to the US embassy, Baghdad international airport, where US troops are based, and Irbil, where a US presence includes 40 military advisers, hundreds of staff evacuated from the Baghdad embassy, and a recently expanded CIA station at the airport.

The US intervention is aimed at clawing back areas lost to the Islamic State including seizing a dam and forcing a mass exodus of religious minorities, leaving them without any food in searing heat.

Officials in Europe and Britain have pledged financial aid to support humanitarian efforts in Iraq.